Extruding a coating of a polyolefin or blends of polyolefins onto a substrate, such as paper or aluminum foil, to form an extrusion coated substrate, is well known in the art. Various polyethylenes and blends of polyethylenes have been widely used as extrusion coating compositions. However, these polyethylene-based coatings must be extrusion coated at high temperatures to effect good adhesion to the substrate and therefore, have several drawbacks.
High temperature extrusion coating processes are not useful with substrates which are temperature sensitive. High temperature extrusion coating processes are also not practical when applying coatings containing additives which are temperature sensitive. The temperature of the high temperature extrusion coating process can be reduced very slightly but then the coating speed must also be reduced considerably to maintain good adhesion. However, high coating speeds are important so as to enable economically attractive operation of extrusion coating equipment.
What is desired, therefore, are polyethylene-based extrusion coating materials which contain thermally sensitive additives that are capable of adhering to substrates while producing substantially uniform extrusion coatings when applied to a variety of substrates, including photographic paper, employing a process which operates at adequate coating speeds at temperatures below those ordinarily used for extrusion coating processes.